In a recent post to DZone.com Dustin Whittle talks about performance in PHP applications and gives you a crash course on some of the basics around it (this is part one of a series).

We all know performance is important, but performance tuning is too often an afterthought. As a result, taking on a performance tuning project for a slow application can be pretty intimidating - where do you even begin? In this series I'll tell you about the strategies and technologies that (in my experience) have been the most successful in improving PHP performance. To start off, however, we'll talk about some of the easy wins in PHP performance tuning. These are the things you can do that'll get you the most performance bang for your buck, and you should be sure you've checked off all of them before you take on any of the more complex stuff.

He talks some about why performance matters and some of the more common practices to introduce immediate performance improvements into your application. His list includes things like: update PHP, use an opcode cache, use autoloading and session optimization. He also talks about using processing queues for blocking work and learning how to use code profiling tools to find the pain points.